A faint infrared object may be the first clue to the long-sought Planet Nine. It was detected in two images of the sky taken 23 years apart, and between the observations it moved by 47.46 arc minutes.
The candidate was discovered by a team from National Tsing Hua University in Taiwan while analyzing data from two space missions. IRAS mapped the sky in 1983, and the Japanese AKARI device made infrared observations in 2006 and 2007.
The results are published in Publications of the Astronomical Society of Australia. The researchers were looking for an object that was moving slowly, emitting a suitable amount of infrared energy, and was located at a huge distance beyond the orbit of Neptune.
The analysis was focused on a planet between 500 and 700 astronomical units from the Sun. One astronomical unit is the average distance between the Earth and the Sun. According to the model used, the sought-after object should have a mass between 7 and 17 times that of the Earth.
After reviewing millions of infrared sources, the scientists found 22 possible matches. Additional selection reduced their number to 13, and inspection of the images left only one object that met the conditions.
Infrared observations are important because such a distant planet would reflect extremely little sunlight. However, it would emit its own heat, which can be detected by spacecraft operating in the infrared range.
The ninth planet remains hypothetical. The idea of its existence is based mainly on the unusual grouping of the orbits of some distant bodies in the Kuiper belt. According to models, this behavior can be explained by the gravity of a large planet located beyond Neptune.
However, the authors of the study do not announce the discovery of a new planet. “The observations with AKARI and IRAS alone are not sufficient to determine the full orbit of this candidate“, they point out.
The next step is to observe the object with the Dark Energy Camera on the 4-meter telescope “Blanco“ in Chile. These observations should show whether its motion is consistent with an orbit that could make it a viable candidate for Planet Nine.